As the level of sophistication has increased in biomedical arts, advances have been made in implantable therapies. Therapies have evolved that involve the precise application of stimulus including electrical stimulus medication. Functional electrical stimulation of the nervous system, for example, can be used to help to restore or maintain some degree of lost sensory and motor function in neurologically impaired individuals. In addition, there are certain specialized applications, such as the treatment of sleep apnea and natural interfaces to amputee prosthesis, where it is necessary to simultaneously monitor and generate electrical and chemical signals in nerves. To this end, various implantable devices have been developed for delivering electrical stimulation to peripheral nerves to influence nerve function.
Several types of nerve cuff electrodes are commercially available. Conventional cuff electrodes, for example, include proximity electrodes that are sutured into position. These electrodes require a relatively high amount of current. Half cuff electrodes are generally C-shaped, while cylindrical electrodes can be spiral, helical, split-cylinder, or chambered cylinders. C-shaped or split cylinder electrodes generally include a cylinder of dielectric material with a bore having sufficient diameter to receive a nerve trunk. Single or multiple annular electrodes can be positioned on the inner surface of the bore for applying electrical stimuli. The electrical stimuli, for example, may be used to provide functional electrical stimulation, to block neural nerve impulses traveling along the nerve trunk, or to cause other effects.
The spiral type of cuff electrode typically includes a self-curling sheet of non-conductive material biased-curl into a spiral. Conductive strips or pads are disposed on the self-curling sheet extending peripherally around the inner surface of the cuff. The conductive segments may be electrically conductive for applying electrical impulses, or fluid conductive for infusing or extracting medications. In use, a first edge of a self-curling sheet may be disposed adjacent a nerve truck around which the cuff is positioned. The self-curling sheet is permitted to curl around the nerve forming an annular cuff. Helical electrodes wind around the nerve like a spring, allowing nerve flex and fluid exchange with surrounding tissue.
Another approach to electrical stimulation of the nervous system involves small wire electrodes, which penetrate the perineurium membrane and are advanced into a fascicle of the nerve within fascicular endoneurium. This method is highly invasive.